A number of catalysts for ammoxidation of propylene have been proposed. Examples of catalysts known to be useful in ammoxidation of propylene include metal oxide systems, such as molybdenum-bismuth catalysts, iron-antimony catalysts, uranium-antimony catalysts, molybdenum-tellurium catalysts, etc., as described in JP-B-36-5870 (corresponding to U.S. Pat. No. 2,904,580), JP-B-37-14075 (corresponding to U.S. Pat. No. 3,152,170), JP-B-38-19111, JP-B-40-24367 (corresponding to U.S. Pat. No. 3,308,151), JP-B-38-17967 (corresponding to U.S. Pat. No. 3,226,422), JP-B-39-8214 (corresponding to U.S. Pat. No. 3,226,421), JP-B-53-18014 (corresponding to U.S. Pat. No. 3,988,359), JP-B-57-26592 (corresponding to U.S. Pat. No. 4,370,279), JP-B-58-2232 (corresponding to U.S. Pat. No. 4,228,098), JP-B-61-26419, JP-B-61-58462 (corresponding to U.S. Pat. No. 4,600,541) and JP-B-51-33888 (corresponding to U.S. Pat. No. 4,503,001), (the term "JP-B" as used herein means an "examined Japanese patent publication"), and U.S. Pat. Nos. 4,495,109, 4,192,776, 3,461,150 and 3,338,952.
Some of them have been applied to practical use on an industrial scale, but they sometimes undergo deterioration after long-term use, resulting in reduced yield of the main product, i.e., acrylonitrile. The degree of deterioration widely varies depending on the structure of the reactor used, reaction conditions, and the like.
Various proposals have hitherto been made to regenerate the deteriorated catalysts. For example, catalyst regeneration techniques which can be applied while conducting the reaction include a method of adding a phosphorus component to the reaction system as disclosed in JP-A-53-90238 (corresponding to U.S. Pat. No. 4,124,631) and JP-A-59-139938 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"); a method of adding tellurium and/or molybdenum as disclosed in JP-A-57-167736 (corresponding to U.S. Pat. No. 4,409,122), JP-A-57-187039 (corresponding to U.S. Pat. Nos. 4,618,593, 4,709,070 and 4,709,071), JP-A-58-139745 (corresponding to U.S. Pat. Nos. 4,618,593, 4,709,070 and 4,709,071), and JP-A-58-140056 (corresponding to European Patent 76,678), U.S. Pat. Nos. 3,168,572 and 4,391,880, and Polish Patent 95,391; a method of adding a molybdenum component as disclosed in JP-A-59-76543 (corresponding to U.S. Pat. No. 4,536,483) and JP-A-59-76544 (corresponding to U.S. Pat. No. 4,757,038); a method of adding an antimony component as disclosed in JP-A-59-90633 (corresponding to U.S. Pat. No. 4,504,599); and a method of adding boron as disclosed in JP-A-59-139940.
Nevertheless, none of these proposals is quite satisfactory from an industrial viewpoint due to disadvantages, such as insufficient effects, insufficient duration of the effects, difficulty in repeated application of the technique, and the like. Hence, industrially applicable techniques for catalyst regeneration have been limited.
In the ammoxidation of propylene for production of acrylonitrile, not only is it important to maintain a high yield of acrylonitrile, but another consideration which is important is by-production of hydrogen cyanide. From an industrial standpoint, a high level of yield of both of these two compounds is required. However, conventional techniques have been developed with the chief object of maintenance of the acrylonitrile yield, and no attention has been directed to maintenance of the hydrogen cyanide yield In other words, difficulty in simultaneously attaining a high level of yield of both acrylonitrile and hydrogen cyanide occurs with conventional techniques.